It’s been more than 200 years since the widespread implementation of the steam engine.
Why is this still the most prevalent means of producing electricity? With things like fusion reactors, why is it so hard to convert the thermal energy into electrical energy?
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Aside from solar cells, the primary way of generating electricity is through rotating magnetic fields. It’s simple and effective. All you need is a magnet and some way of turning it.
Water is an ideal way of doing this. It’s plentiful and can go from liquid to gas and back within a range of easily achievable temperatures. So all you need to worry about is how to make water do this.
Steam Rankine cycle (vs other heat engine cycles) is very good up to about 550 C which is near the creep strength limit of steel. Going higher requires exotic materials or power cycles (gas Brayton or sCO2) and only gives marginal gains. Capital costs outweigh efficiency gains.
It’s better than other options for iron based materials. More expensive materials aren’t worth the gains.
> It’s been more than 200 years since the widespread implementation of the steam engine. Why is this still the most prevalent means of producing electricity? With things like fusion reactors, why is it so hard to convert the thermal energy into electrical energy?
Steam is used in most fission reactors and unless there is some fundamental discovery it will be used in fusion reactors as well. When something is cheap and efficient why change it?
Imagine 100 or 200 years from now you somehow are still alive and able to think rationally and someone asks you “why are we still using electricity and electronic devices, …?” How might you answer their question? Can you see how you question today is similar?
It is efficient, cheap and easy to scale.
For generating power your options are:
1. __Steam turbine, 30-40% efficient__. Used by coal/fossil fuels, nuclear, concentrated solar power, geothermal, etc.
2. __Combined cycle, 60% efficient__. This works for natural gas has 2 turbines one is NG burning the second is a steam turbine using the heat from the NG turbine so you get about double the efficiency. This is part of why NG is cleaner than coal (but still not very clean). Its generally more expensive to build and more complex though.
3. __Diesel generator, 30-40% efficient__. But also much more maintenance, costs more to build, needs specific fuel, can be very expensive at electric grid scale.
4. __Thermocouple, 5-10% efficient__. These are both expensive and inefficient. They produce electricity when heat is transferred through them via the [thermoelectric effect](https://en.m.wikipedia.org/wiki/Thermoelectric_effect). They are mainly used by NASA to power rovers and probes with the heat of nuclear decay (on the hot side and cold space/mars on the cold side).
5. __Solar PV, ~20% efficient__, but very cheap and who cares it’s not like we are wasting sunlight.
So for fusion 2 and 3 are not options, 5 would be vaporized instantly, leaving steam and thermocouple. I’d take cheap and efficient steam turbine over a thermocouple any day.
Also, Hydroelectric is ~90% efficient which is awesome for pumped hydro grid storage.
After thousands of years , we’re still boiling water to make electricity. We just need to find a safe, cheap way to do it. I’m not here to debate nuke plants. I think they can work.
Keep in mind that just because a technology is old does not mean it mist be outdated. The inclined plane. The lever. The wheel. These technologies predate steam engines by millenia and yet there they still are, doing their jobs well enough that there’s simply no need or advantage in recreating them. The steam turbine is similar. Water plus heat equals a great way to spin a generator.
Steam is very efficient because steam cycles operate on heat so it can use most of the chemical energy in its fuel. When a fuel is burned, it releases energy as heat, and if contained in a piston, it releases pressure as the pressure of expanding gasses. A gasoline internal combustion engine uses the pressure expanding gases of gasoline combustion to push pistons and turn the engine, but hardly uses any of the heat produced, so that energy is lost. A steam engine, on the other hand, does not contain its fuel and so almost all of the energy is turned to heat. The engine then uses that heat to turn the water into steam, which then turns a turbine. So a steam engine could, in theory, utilize all of the energy released by its fuel. In reality, heat is still lost, but its still a very efficient way to use fuel.
Steam is used because it’s a great tool for converting thermal to mechanical energy (which then drives generators).
Other methods exits for direct electrical generation (fuel cells, radio isotope thermal generators, etc) but few are cost effective at scale.
Because it’s a cheap working fluid, and combined cycle steam plants are rather efficient (65-70%), essentially. The ability to pressurize steam vapor to high pressure super heated conditions (~1100F, ~4000psi range) in modern steam plants make it great for pushing around highly engineered turbine blades, which push a generator. It’s a quite mature technology at this point, so it has quite high fidelity and predictability, and it’s well known how to build and replicate it in various locales. I studied mechanical engineering, so maybe I’m biased based on how big of a subject it was for us, but it has been a difficult technology to provide a clear alternative for given how reliable it is.
It’s probably on it’s way out, in some senses, as wind and solar is now less expensive and construction of those has become essentially the bulk of new energy infrastructure being built. That said, given the fact that steam power plants can be retrofitted to use molten salt as an energy storage fluid heated by excess wind, solar, etc production, we may see them used essentially as grid batteries going forward instead of becoming irrelevant
Water takes a lot of energy in when its being warmed up, and it needs to lose a lot of that energy to cool down. It’s not only useful because of how much energy it can hold onto, but because when it turns into steam that energy means its exerting a lot of pressure when its not allowed to easily escape from that space. The combination of reliably holding on to a lot of energy and exerting a lot of pressure is why it’s used to turn turbines in most power plants for energy.
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